I am 18 ½ weeks pregnant and have had a previous pregnancy with trisomy 13, which resulted in fetal demise. I have had a stage II ultrasound this time at 15 ½ weeks and everything looked good. The geniologist looked at the ultrasound and reported there were no stigmata of a trisomy, 13 or otherwise. My question is related to my AFP results, which were abnormal. My OB suggests an amniocentesis, but since 95% to 98% of these results are wrong, I do not wish to risk the amnio. I am scheduled for another ultrasound in 2 weeks. Can I tell or can the doctor see if the baby has Down’s syndrome by looking at that?

Diagnosis of chromosomal anomalies by amniocentesis is highly accurate. Although there are no major studies on error of amniocentesis, it has been shown that errors in diagnosis occur only 0.1% to 0.6 % of the time. Therefore, most of the time results from amniocentesis are correct. If you are worried about the potential risks of amniocentesis–which include preterm labor, rupturing of the membranes, and fetal loss–you should keep in mind that these complications occur in 1 in 200 amniocenteses.

If you decide against amniocentesis, your doctor can look for the stigmata of Down’s syndrome on your ultrasound. Keep in mind, however, that this is much less specific than amniocentesis. Speak with your doctor further about the risks and benefits of each of these options.